A readily available supply of plasma and whole blood is an essential requirement of any medical trauma treatment facility. Since plasma can be stored at room temperature for a matter of only a few hours before spoilage occurs, it is conventional practice to freeze blood components. Whole blood can be stored only forty days before spoilage occurs and hence must be frozen if storage for longer periods is anticipated. Typically, plasma and whole blood are frozen within six hours after collection, in polyvinyl chloride bags holding about 300 milliliters. The fresh-frozen plasma is subsequently stored at temperatures of around -30.degree. C., and fresh-frozen whole blood is stored at temperatures of around -80.degree. C. When properly frozen, blood and blood components may be stored for up to ten years.
While the procedure of fresh-freezing blood and blood components has essentially solved the problems of storage, the process of thawing the product for use presents certain difficulties. When whole blood or platelets are being thawed, possible damage to cells during thawing is a major concern. While post-thaw viability of cellular structures is not of concern in thawing plasma, the viability of coagulation proteins is of primary importance. The most widely accepted method of thawing fresh-frozen blood and blood components comprises immersing the bag in a warm water bath. By completely surrounding the bag in a 30.degree. C.-37.degree. C. water bath and agitating it periodically, a single bag or "unit" of frozen plasma may be thawed usually in thirty to forty-five minutes.
This procedure presents a number of problems. First, immersing the bag in a non-sterile water bath may contaminate the bag ports, such that the thawed blood or blood components are tainted as they are withdrawn from the bag. Immersing the bag in a warm water bath can also cause any labels affixed to the bag to become detached. Even if the labels remain attached to the bag, the warm water bath often causes the labels to become wrinkled, such that it becomes impossible to scan a bar code which may be imprinted on the label. Additionally, any interruption in the integrity of the bag can permit an exchange of water and plasma, thereby contaminating both the product and the water bath. The most common form of interruption in the integrity of the bag is "edge damage" resulting from impact of the bag edges with any hard object while at low temperatures. This results in fracture of the PVC bags in 5-10% of all bags produced. Further, the water bath process cannot be accelerated, such as by exposing the blood or blood components to a higher temperature bath, since subjecting frozen plasma to any larger thermal gradient in an effort to speed up the procedure can result in physical stress and possible damage to the normal protein configuration of the plasma, and since subjecting whole blood or platelets to a higher thermal gradient can possibly damage cellular structures. The requirement of a thawing period of from thirty to forty-five minutes renders the use of frozen blood or blood components impractical for emergency trauma cases, where the patient may have an immediate need for the product and cannot affort the luxury of waiting for frozen blood or blood components to be thawed. Medical facilities cannot anticipate possible needs of blood and blood components by thawing a number of units in advance, since the requirement that each unit be typed and cross-matched to the specific patient for which it is intended would require thawing an inordinate number of units which would not be used. Furthermore, since the product cannot be safely refrozen once thawed, units which are thawed in anticipation of possible use must be discarded if the anticipated use does not arise.
Accordingly, there is a need to provide a hygienic method and apparatus for the thawing of fresh-frozen blood and blood components which does not expose the ports or the contents of the bag to the possibility of contamination.
There is also a need to provide a method and apparatus for the thawing of fresh-frozen blood and blood components which is sufficiently rapid that the product can be kept frozen until only moments before it is actually needed.
A number of efforts have been made to adapt microwave ovens for thawing frozen blood components which are contained in a bag. Some of these efforts have involved attempts to adapt a conventional cavity-type microwave oven, of the type widely used for cooking foods, for use in thawing such blood components. However, conventional prior art microwave blood-thawing devices tend to thaw the blood unevenly, which can result in overheating localized portions of the blood while other portions of the blood remain frozen.
The apparatus disclosed in my prior U.S. Pat. No. 4,874,915 overcomes many of the shortcomings associated with previous devices for thawing blood and blood components with microwave illumination. The bag of frozen blood or blood components is placed within a membrane surrounded by a liquid dielectric material which is impedance-matched with the frozen product. The membrane and liquid dielectric material readily conform to the surface of the blood bag to eliminate impedance mismatches at the various interfaces. In the disclosed embodiment, a substantially uniform magnetic field is created by employing a waveguide which supports only odd-numbered harmonic wavelengths and by utilizing an RF lens to disperse the waves across the width of the blood bag. Thus, nonuniform heating resulting from standing waves caused by reflections or from uneven illumination is substantially eliminated, thereby providing uniform heating of the frozen product.
However, the apparatus and method disclosed in my aforementioned U.S. Pat. No. 4,874,915 suffers certain disadvantages common to microwave thawing devices, namely high cost, mechanical complexity, and limited portability. In certain instances, small medical facilities which may have a need for a readily available supply of blood or blood components may not be able to afford the considerable cost of a microwave blood warming device. Further, the mechanical complexity necessitates maintenance costs and may possibly cause the unit to break down at an inopportune time. Finally, microwave thawing devices do not lend themselves to ready portability.
Thus, there is a need to provide a method and apparatus for the rapid thawing of blood and blood components which can be made available to medical facilities at a relatively low cost.
There is also a need to provide a method and apparatus for the rapid thawing of blood and blood components which is mechanically simple so as to eliminate maintenance costs and substantially reduce the possibility of malfunction at an inopportune time.
There is yet another need to provide a method and apparatus for the rapid thawing of blood and blood components which is highly portable.
Conventional blood freezing apparatus presents further problems with the length of time required to freeze whole blood and plasma contained therein. Factor 8, the primary clotting factor in blood, deteriorates rapidly at room temperature. Absent expensive high-speed liquid immersion freezing equipment, freezing whole blood or plasma in a conventional blood freezing apparatus does not occur rapidly enough to prevent deterioration of a significant proportion of the Factor 8.
Thus, there is a need to provide a method and apparatus for freezing whole blood and plasma which is sufficiently rapid that deterioration of Factor 8 is reduced.